Bearing type wheel speed sensors are commonly used in brake control systems, antilock brake systems (ABS), traction control systems, differential lock-up systems and the like to provide a control signal representative of wheel rotational speed to a controller such as a microprocessor based electronic control unit. Typically, such sensors are electromagnetic in nature and rely on a variable reluctance magnetic flux path to produce the wheel speed signal.
Annular rotational speed sensor assemblies having multi-toothed stators which surround a similarly multi-toothed rotor, or vise versa, are known in the art. Annular multi-toothed assemblies are preferred for sensing low wheel rotational speeds since they tend to provide high sensitivity as well as high signal to noise ratios. Examples of such wheel speed sensors may be seen by reference to U.S. Pat. Nos. 5,111,098, 5,227,719, 5,281,911, 5,291,130 and 5,336,995.
Some problems encountered with prior art wheel bearing speed sensors include unwanted magnetic flux loss to the housing and bearing assemblies, inefficient flux transfer and low sensitivities under certain conditions. Prior art attempts at overcoming some of these problems have resulted in burdensomely complex fabrication and assembly techniques used to achieve desired performance characteristics. What is therefore needed is a simple, easily manufactured and low cost wheel bearing speed sensor which will, at the same time, provide desirable performance characteristics. Such a sensor should provide an efficient flux path, have minimal flux loss and have high sensitivity. In addition, the sensor should be easy and inexpensive to manufacture by maintaining structural simplicity and incorporating inexpensive materials.